Development of NAMPT Positive Allosteric Modulators as Potential Alzheimer’s Disease Therapeutics

Therapies directly targeting hallmark Alzheimer’s Disease (AD) pathophysiology amyloid β and hyperphosphorylated Tau have been unsuccessful, so an alternative drug target is desperately needed. Nicotinamide phosphoribosyltransferase (NAMPT) is one such target. Increasing catabolism of nicotinamide adenine dinucleotide (NAD) with age, leading to NAD depletion, impacts pathways crucial to neuronal function, neural reserve, and resilience to AD. Restoration of depleted NAD by supplementation with NAD biosynthetic precursors improves multiple cellular systems perturbed in AD models. However, the therapeutic potential of NAD supplements in AD is unclear due to homeostatic and pharmacokinetic mechanisms. An efficient way to increase NAD that avoids such issues is to activate NAMPT, which catalyzes the rate-limiting step in NAD biosynthesis. NAMPT activators can increase NAD production and prevent homeostatic inhibition, allowing for effective NAD enhancement. We hypothesize that by activating NAMPT, increased NAD levels will support neuronal resilience to aging and AD-associated dysfunction. To test this hypothesis, NAMPT activators were identified by high throughput screen (HTS), and synthetic method development, derivatization, and in vitro characterization were performed. This led to an increase in cellular (THP-1) NAD enhancement by 70% over the hit. Our compounds bind to an allosteric channel and are therefore more precisely termed NAMPT positive allosteric modulators (N-PAMs). This was followed by development of, and N-PAM characterization in, cell-based oxidative stress resistance models relevant to aging and AD. The protective activity of N-PAMs was assessed in a neuronal cell line (HT-22) stressed with menadione, glutamate, or tumor necrosis factor alpha (TNF⍺) to model oxidative stress, excitotoxicity, and neuroinflammatory signaling damage. In these models, N-PAMs exhibit a marked ability to prevent the accumulation of reactive oxygen species (ROS). Widespread cellular damage in aging and AD is caused by elevated levels of ROS. Their mitigation by N-PAMs in neuronal cells supports the relevance of this therapeutic strategy to AD and further investigation of these agents as therapeutics in all ROS-mediated disease processes.